M. Mariotti. Proceedings of the 22nd Conference of the International Group for the Psychology of Mathematics Education, 1, page 180--195. Stellenbosch, South Africa, PME, University of Stellenbosch, (July 1998)
T. Schummer, S. Lukosch, and R. Slagter. Groupware: Design, Implementation, and Use, 11th International Workshop, CRIWG 2005, Lecture Notes in Computer Sciecne 3706, page 73-88. Berlin Heidelberg, Springer-Verlag, (2005)